1. Field of the Invention
The invention relates to the elimination of deleterious compounds such as nitrogen oxides, carbon monoxide and residual hydrocarbons, which are present in the exhaust gas from engines provided for vehicles such as automobiles, trucks, buses, motorcycles and tractors. The invention prevents the discharge of these noxious components into the atmosphere, and thereby prevents air pollution. Application of the invention to engines in general will be understood to encompass other types of combustion devices and engines such as gas turbines, diesel engines and the like.
2. Description of the Prior Art
In recent years it has been recognized that the exhaust gas discharged from internal combustion engines is a serious source of air pollution, especially in metropolitan areas. In some cases, a so-called smog is generated due to atmospheric inversions and accumulation of such exhaust gases in the atmosphere. Recent attempts to prevent such air pollution have concentrated on the destruction or elimination of noxious components by catalysis, especially by catalytic reduction of nitrogen oxides followed by admixture of secondary air into the exhaust gas and catalytic oxidation of residual hydrocarbons, carbon monoxide, etc., in various types of apparatus especially designed for this purpose. Improvements in active catalytic agents for this function are described in U.S. Pat. Nos. 3,053,773; 3,316,057; 3,429,656; 3,476,508 and 3,310,366, and U.S. patent application Ser. No. 45,576 filed June 11, 1970 now U.S. Pat. No. 3,701,822. Copper-bearing catalysts are generally U.S. Pat. Nos. 3,398,101; 3,447,893; 3,493,325; 3,133,029 and 2,025,140 and U.S. patent application Ser. No. 55,998 filed July 17, 1970, allowed Dec. 30, 1971, and abondoned in favor of U.S. Pat. application Ser. No. 237,516 filed Mar. 23, 1972 and now allowed and issued as U.S. Pat. No. 3,840,642. Two-stage apparatus for carrying out the process with interstage air injection is described in U.S. patent applications Ser. Nos. 33,359 filed Apr. 30, 1970 now U.S. Pat. No. 3,656,915 and 143,401 filed May 14, 1971 now U.S. Pat. No. 3,733,181.